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Gloss Going Matt


Stephen

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OK I am assuming I screwed up although I still wonder how that could happen as careful as I am. I made the recipe listed below first as a 400 gram test batch that came out perfect with just the right surface, fit and break that we were looking for.

 

The base is transparent and we wanted to take the color down a couple of shades so I made a 10,000 batch and split out 4 small (100 gram equivalent) test batches from that and adjusted the additives a point a shot for two of them and then did a couple with two different mason stains as additives. The goal was to create a small half dozen color palate using this transparent base for a line of hand painted pieces that needs a surface that allows detail to show through but have a color tint instead of just a clear coat on top. 

 

I was expecting issues with possible clouding with the stains or a trend toward opaque. I did not expect the glaze to go from a high gloss to completely matt. One possibility because my scale tops out before the weighs I need for 10k grams I have to break each measurement in half so it is possible, maybe, I put 30% of one and 10% of something else. This is the only possible mistake I can see and since I am so careful It would surprise me if that's the case.

 

Can anyone see something else in the recipe that might cause this or have a suggestion of an adjustment that might get me back to gloss? I did use a new bag of frit 3134 but all the other ingredients were on hand and the ball clay was OM4.

 

 * All test were fired in the same 1cf test kiln with a controller fired ramp to cone 5 with 15 minute hold and controlled cool down to 1200 degress.     

 

Honey Amber ^6 Oxidation Glaze

Dolomite 20
Frit 3134 20
Flint 20
Spodumene 20
Ball Clay 20

 

additives:
Manganese Dioxide 3
Red Iron Oxide 5

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Neil,  yeah that probably would have been the best way, I always worry I will grab a a bad 100gram pull from the mix. I split out the same amount of wet base that I get from a 400 gram dry test batch an then split that into 4 equal parts. It worked out to 222 grams mixed weight per test batch and that matched up pretty close to the one 100 gram container left untouched from the first test. I think it really is pretty dead on to what I would have mixed into 100 grams batches from the scratch.  

 

oldlady, the 2 stains are mason evergreen 6200 and sky blue (don't see it on the chart). Since it was matt on both stains and the reduced oxide additives I dismissed the stains as having caused it. 

 

Thanks guys, I appreciate any input. I am going to do some research tonight and see if something pops out.

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I'm very unclear why you did this wet?

Most mistakes are from measuring wrong-I have made more than you can imagine.

when working with large 10,000 gram batches make a measuring check list.

Also buy a cheap electronic scale for those large batchs so you can wieghh the ingredients all at once.

It will save you headaches.

Mark

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Hi Mark,

 

Yes I am going to add a larger scale so I don't have to split into two when I am making a 10k batch. The one I have is pretty expensive but tops out for large batches on some of the large percentage ingredients and that is certainly an area ripe for mistakes and this might be one of them. 

 

I do use checklist style worksheet for every batch, test and production. I used one for this as well and that's why I am so skeptical that I made a measuring mistake. If you look at the recipe the base is 5 ingredients of 20% each so each one went in 10% at a time and a check mark on the sheet. if I screwed up then something likely got 10% and the next one got 30%.

 

I was doing it wet because it was unplanned. I had run a round of test on a 400 gram test batch and was going to make a 10k batch of the Honey Amber. I decided to hold off on the oxides and do another round of test with less oxide for a lighter shade and then decided to also do a couple with stains. I could have just pulled a 100grams of the mixed dry I guess but thought it was more likely to be an even mixture if I went ahead and mixed it up really well. I did explain my very convoluted reasoning as to why I think it was OK but yeah that may well be the problem. I am going to fire tonight from just the base with the original oxides and see if it fires gloss.  

 

Thanks!  

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no witness cones. we do put htem on each shelf in the production kiln but I must admit I have not been using them in the small test kilns. I will start doing that. These two test were both done a day apart in the same test kiln using the same firing schedule so I assume they fired the same but it is possible they didn't. Life got in the way on firing another test this weekend but will put cones in the next firing to check that. Thanks!

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With out test witness cones you really are flying blind.

May as well spray paint your car windshied as an analogy and go for a high speed drive.

without the cones is just a guess what really happened.

My guess is its fired cooler-hence the matt

Mark

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true, on the cones and no real excuse.  I will do so going forward. The test kiln is/was a new kiln five years ago with the same electronic controller as the large production kiln and I guess I just never implemented using cones in it for my test, should have but didn't. We load a cone pack for every production load. I have never really questioned the firing in the test kiln before as my test batches and then the ones that I make into large batches and fire in the production kiln have always matched up. Not a good reason but the only one I have  :rolleyes:  These two test though were both done in the same test kiln a day a part using the same programmed in firing schedule.

 

I will be re-firing this week and will put some test from both the one that fired gloss and the one that fired matt in the same load so I can tell you definitively after that whether firing was the cause.

 

I sure hope it was!

 

In thinking this through though, one thing that is/was different with these two test is that the little 1 cf  kiln is not vented and I usually leave the top plug out until the kiln is above about 1200 but I am not real regimented about when I do this. It fires overnight with me checking on it off and on and then plopping in the top plug if it's north of 1200. this might be 1250 or 1900 depending on when I check in on it. In such a small space could that difference cause a gloss to go matt?  I always worked from the premise that the program should have kept with the controlled ramp up, 15 minute hold at cone 5 and cooling ramp down to 1200 so I figured it would mature the same regardless of when I put the top plug back in. This is the one thing different about the two test firings.

 

Putting one from each of the test batches in the same firing should shed some light on that as well because if the test both go gloss or both go matt then its pretty much positive its firing and not ingredients, right? If the original fires gloss as it should be and the test form the large batch is matt then its ingredients and that is either me screwing up my measurements or the one ingredient that was bought from a different supplier (the frit) is bad or different.  

 

I'll post back after I have re-fired.

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I plunked the recipe into Insight and played around with increasing and decreasing the ingredients just in case you made an error in the weighing out like you mentioned was the possibility. If you had put  only 10 silica in and 30 spodumene then the Si:Al ratio goes from 8.57 to 6.38 which along with the slow cool could be enough to make a matte glaze. Also, if the error was with the OM4 ball clay the the Si:Al ratio is 6.37 ( 10 silica, 30 ball)

 

Does it feel like an alumina matte, or a silky / buttery matte?

 

I would include a test tile with no colour additives as a baseline.

 

Also, do you need to slow cool if you are going for a gloss?

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